When the air conditioning load in the compartment of a car is decreased by an air conditioning system, or the temperature in the compartment of the car is below the predetermined temperature, the displacement of the compressor, and therefore the compression ratio of the compressor, can be decreased.
A scroll type compressor which can vary the compression ratio is well known in the art. For example, U.S. Pat. No. 4,505,651 and U.S. Pat. No. 4,642,034 show such compressors.
However, in U.S. Pat. No. 4,505,651, the compression ratio change is not sufficient. Also, in the mechanism shown in U.S. Pat. No. 4,642,034, the temperature of the discharge fluid increases abnormally when the compressor operates at high speeds.